Method of affecting mixture formation and charge motion in an engine cylinder

ABSTRACT

A method of affecting the mixture formation and motion of a charge in an engine cylinder during a suction cycle of a gas intake valve of the cylinder. The suction cycle has a first cycle portion and a subsequent, second cycle portion. The method includes the following steps: introducing air and fuel into the cylinder during the suction cycle; maintaining, during the first cycle portion, the gas intake valve in a first open position at full valve stroke in which the gas intake valve has a fully open cross-sectional flow passage area; and maintaining, during the second cycle portion, the intake valve in a second open position at a partial stroke of the gas intake valve. The partial stroke is less than one half of the full stroke; and in the second open position the gas intake valve has a partially open cross-sectional flow passage area.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a division of application Ser. No. 09/123,578filed Jul. 28, 1998.

[0002] This application claims the priority of German Application No.197 33 139.4 filed Jul. 31, 1997, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0003] For influencing the formation of mixture and the motion of acharge in cylinders of externally ignited piston-typeinternal-combustion engines, published International Application WO91/14858 describes means in the region of the intake valves for acontrollable flow deflection as the intake gas passes from the intakeopening into the cylinder. An insufficient mixture formation is causedby an insufficient or missing vacuum in the intake pipe due to a poorfuel vaporization and cannot be improved at a fully open cross-sectionalflow passage area of the valve because of the low intake velocity.Slides, gates, pivotal nozzles and the like are proposed as means fordeflecting the flow. Such elements are arranged in the channel-likeintake port immediately in the region of the intake opening and areoperated by suitable setting means as a function of the operationalcondition of the engine. The setting means are actuated by a controldevice to so deflect the inflowing air/fuel mixture (hereafterdesignated as gas flow) under certain operational conditions that duringthe suction stroke within the cylinder chamber a turbulence (vortex) isgenerated whose rotary axis extends essentially transversely to thecylinder axis. It is a disadvantage of such an arrangement that the flowdeflecting elements are disposed and supported in the intake portimmediately upstream of the intake opening, that is, in a region inwhich only little room is available for additional structuralcomponents.

SUMMARY OF THE INVENTION

[0004] It is an object of the invention to provide an improved method ofthe above-outlined type which affects the mixture formation and thecharge motion in engine cylinders without the need of encumberingstructural components.

[0005] This object and others to become apparent as the specificationprogresses, are accomplished by the invention, according to which,briefly stated, the method of affecting a mixture formation and motionof a charge in a cylinder of an externally ignited internal-combustionengine during a suction cycle of a gas intake valve of the cylinder isperformed such that during a beginning (leading) and/or terminal(trailing) portion of the suction cycle the valve is opened andmaintained open only partially at a valve stroke which is less than onehalf of its full stroke and for the remainder of the suction cycle thegas intake valve is fully open at a full valve stroke.

[0006] By changing the cross-sectional area of the valve flow passage asoutlined above, the mixture preparation and charge motion may beadvantageously affected. By initially providing only a smallcross-sectional flow passage area, the mixture preparation is improvedand subsequently, by opening the valve to the full cross-sectional flowpassage area, the combustion chamber is filled with the fresh mixture.In the first phase of the piston stroke the fuel/air mixture flows intothe combustion chamber at a high velocity through the only slightlyopened cylinder valve, positively supporting the mixture preparation andmixture homogenization. The charge quantity required for obtaining adesired load point may, however, not be obtained with a constantly smallcross-sectional area of the flow passage so that during the same openingphase (suction cycle) the cylinder valve is fully opened by a suitablecontrol system to thus ensure an optimal filling of the combustionchamber with a fresh mixture.

[0007] The method according to the invention may be performed in severalways. Thus, according to a preferred embodiment of the invention, in thebeginning the open period of the gas intake valve during a full“closed-open-closed” suction cycle, the valve is maintained onlypartially open and only for a short period, at the end of which thevalve is closed and shortly thereafter re-opened to the full flowpassage area. In this manner with a first, partial mixture charge amotion is initiated in the cylinder chamber at an increasing vacuum, sothat subsequently, at full valve opening, the full charge quantity mayflow in with high speed by virtue of the increased vacuum.

[0008] According to another preferred embodiment of the method of theinvention, the gas intake valve is first opened to the full crosssection, thereafter maintained at a partially open state and then fullyclosed. With such a method too, it is possible to introduce a residualquantity of fresh gas at high velocity into the cylinder towards the endof the suction cycle and to thus favorably affect the charge motion inthe cylinder. As a variant, the valve may be fully closed after theinitial full opening and thereafter opened and maintained briefly in apartially open state.

[0009] The above-outlined different modes of operation may be combinedwith one another dependent upon the load conditions, and it is alsofeasible to control, in engines having a plurality of gas intake valvesfor each cylinder, all or only a single valve of the cylinder with themethod according to the invention.

[0010] While it is in principle feasible to obtain the inventive suctioncycle characteristics of the cylinder valve by mechanical drives, themethod according to the invention finds particularly advantageousapplication in piston-type internal-combustion engines whose cylindervalves are operated by electromagnetic actuators in which the controlperiods are freely variable. Thus, by different opening and closingmoments for the individual suction cycle stages (partially open or fullyopen cross-sectional flow passage area), different open periods for thesuction cycle stages can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a graph illustrating the stroke S of a gas intake valveas a function of the crankshaft angle according to a conventional valvecontrol method.

[0012]FIGS. 2, 3, 4, 5 and 6 are graphs illustrating the stroke S of agas intake valve as a function of the crankshaft angle according to fivepreferred embodiments of the valve control method according to theinvention.

[0013]FIG. 7 is a schematic axial sectional view of an example of anelectromagnetic actuator for performing the method according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In the course of a conventional control of a suction cycle of anintake valve as illustrated in FIG. 1, the valve is moved directly intoand maintained in a full-stroke position for a given period so that thegas may flow into the combustion chamber through a fully opencross-sectional area of the valve flow passage. Thereafter, the gasintake valve is fully closed. A valve opening characteristic of thistype, particularly at partial load conditions, does not yield a fullysatisfactory mixture preparation in otto engines.

[0015] If, as shown in FIG. 2, during a leading end portion of thesuction cycle, the valve is opened only with a short stroke and ismaintained in such a partially open position, then, corresponding to thepredetermined vacuum, the gas may flow through the small cross-sectionalflow passage area with high speed into the combustion chamber so thatsubsequently, upon a full opening of the valve, the combustion chamberreceives the full charge fill and the vortex induced at the beginning ofthe suction cycle improves the mixture preparation and the motion of thecharge. Such partial opening (partial stroke) of the valve is, accordingto the invention, less than one half of the full stroke of the valve.

[0016] The same effect may be achieved if, as shown in FIG. 3, the valveis opened during the short-period leading end portion of the suctioncycle with a small stroke, then the valve is closed and after a delay itis again opened with a full stroke to the fully open cross-sectionalflow passage area. Since the piston, during the short closed period ofthe valve, continues to move, during such period the vacuum in thecombustion chamber increases so that the residual gas may flow into thecombustion chamber with a correspondingly increased velocity.

[0017] The stroke curves according to FIGS. 4 and 5 represent respectivereversals of the cycle courses described in FIGS. 2 and 3; as a result,during the trailing end portion of the suction cycle the inflowing gasagain may flow into the combustion chamber with a high velocity.

[0018]FIG. 6 shows a suction cycle curve which essentially is asuperposition of the curves shown in FIGS. 2 and 4. Thus, during aleading end portion and a trailing end portion of the suction cycle, theintake valve is maintained open for a short period of time at apartially open cross-sectional area of the flow passage.

[0019]FIG. 7 illustrates an electromagnetic actuator 1 operativelycoupled with a cylinder valve 2. The electromagnetic actuator has anarmature 3 associated with a closing magnet 4 and an opening magnet 5.Both magnets are connected with a non-illustrated electronic controldevice so that upon alternating controlled energization of the twoelectromagnets the armature 3 may move back and forth between the twoelectromagnets 4 and 5 against the resetting force of an opening spring6 and an oppositely acting closing spring 7. The armature 3 assumes itsrespective setting position by lying on the pole face 8 of therespective electromagnet 4 or 5. In the shown example, the two resettingsprings 6 and 7 are of identical design so that in the de-energizedstate of the electromagnets 4 and 5 the position of rest of the armature3 is half way between the pole faces 8 of the two electromagnets 4 and5.

[0020] If, as shown in FIG. 7, the closing magnet 4 is in an energizedstate, the armature 3 lies against the pole face 8 of the closing magnet4 and retains the intake valve 2 in its closed position. If the currentto the closing magnet 4 is switched off, then the force of the openingspring 6 moves the armature, together with the gas intake valve 2 in thedirection of the opening magnet 5 against the increasing force of theclosing spring 7. Upon energizing the opening magnet 5 at apredetermined controllable moment as the armature 3 passes the positionof rest, a corresponding magnetic field builds up which captures thearmature 3 and moves the same into a contacting position with the poleface 8 of the opening magnet 5 against the increasing force of theclosing spring 7. After an open period determined by the control device,the opening magnet 5 is de-energized and thereafter the closing magnet 4is energized, causing the armature 3 again to move into the closedposition as shown in FIG. 7 and thus the gas intake opening is closed.Such a stroke course (suction cycle) corresponds to that described inconnection with FIG. 1.

[0021] In the illustrated embodiment, the resetting spring 7 acts on aspring seat disk 19 connected with a valve stem 18 of the gas intakevalve 2. The valve stem 18 and the guide rod 15 of the armature 3 are ofseparate (divided) construction.

[0022] An additional opening magnet 12 which is associated with theopening magnet 5 has an armature 13 arranged on that side of the magnetwhich is oriented away from the pole face 8. The armature 13 may beguided, for example, in the yoke of the opening magnet 5. The armature13 is maintained in its position of rest by a holding spring 14. Thedistance of the armature 13 from the pole face 20 of the additionalopening magnet 12 determines the extent of a reduced opening stroke suchas described in connection with FIGS. 2-6.

[0023] As, in an uninterrupted energized state of the closing magnet 4,the cylinder valve 2 is held in the closed position by the resettingspring 7, the additional magnet 12 may be energized which causes motionof the armature 13 and thus the intake valve 2 which is opened only toan extent which corresponds to the predetermined distance a extendingfrom the armature 13 (when in engagement with the closing magnet 4) tothe pole face 20. Such an open state of the valve 2 lasts for theduration of the energization of the additional magnet 12. If theadditional magnet 12 is de-energized, the gas intake valve 2 is againclosed by means of the resetting spring 7. If subsequently the closingmagnet 4 is de-energized to achieve a full opening the valve 2, thesuction cycle illustrated in FIG. 3 is obtained.

[0024] The additional magnet 12 may be controlled such that first, asdescribed earlier, the gas intake valve 2 is opened and maintained openwith a small stroke. If subsequently the closing magnet 4 isde-energized and the opening magnet 5 is accordingly energized, thesuction cycle curve according to FIG. 2 is obtained.

[0025] The suction cycle curves shown in FIGS. 4, 5 and 6 too, may beobtained by a suitably timed energization and de-energization of theelectromagnets 4, 5 and 12.

[0026] The open periods for the partial stroke as well as for the fullstroke and the relationship of these open periods to one another may bepredetermined by a corresponding design of the engine control for therespective load conditions.

[0027] The method according to the invention is not limited to gasintake valves operated by an electromagnetic actuator. In principle, thesuction cycle curves according to the invention may be obtained by anytype of actuator structure which make possible a stepped stroke motionof the gas intake valve. It is particularly advantageous to useactuators which may be freely controlled as it is the case inelectromagnetic actuators.

[0028] It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

1. A method of affecting a mixture formation and motion of a charge in acylinder of an externally ignited internal-combustion engine during asuction cycle of a gas intake valve of the cylinder; said suction cyclehaving a first cycle portion and a subsequent, second cycle portion; themethod comprising the following steps: (a) introducing air and fuel intothe cylinder during said suction cycle; (b) maintaining, during saidfirst cycle portion, said gas intake valve in a first open position atfull valve stroke in which said gas intake valve has a fully opencross-sectional flow passage area; and (c) maintaining, during saidsecond cycle portion, said gas intake valve in a second open position ata partial stroke of said gas intake valve; said partial stroke beingless than one half of said full stroke; and in said second open positionsaid gas intake valve having a partially open cross-sectional flowpassage area.
 2. The method as defined in claim 1 , wherein said step(c) comprises the step of directly moving said gas intake valve intosaid second open position from said first open position.
 3. The methodas defined in claim 1 , further comprising the step of fully closingsaid gas intake valve upon ending step (b) and before starting step (c).4. The method as defined in claim 3 , further comprising the step ofmaintaining said gas intake valve closed for a period between steps (b)and (c).
 5. A method of affecting a mixture formation and motion of acharge in a cylinder of an externally ignited internal-combustion engineduring a suction cycle of a gas intake valve of the cylinder; saidsuction cycle having a leading cycle portion, a trailing cycle portionand an intermediate cycle portion; the method comprising the followingsteps: (a) introducing air and fuel into the cylinder during saidsuction cycle; (b) maintaining, during said intermediate cycle portion,said gas intake valve in a first open position at full valve stroke inwhich said gas intake valve has a fully open cross-sectional flowpassage area; and (c) maintaining, during said leading and trailingcycle portions, said gas intake valve in a second open position at apartial stroke of said gas intake valve; each said partial stroke beingless than one half of said full stroke; and in said second open positionsaid gas intake valve having a partially open cross-sectional flowpassage area.